This invention relates to a switch having a locking mechanism and equipped with a device for preventing erroneous operation. More particularly, the invention relates to a switch of the type described in which the lock is released only by turning a rotary knob integrated with an operating portion, and in which inadvertent open-and-down movement of a switch operating member is prevented.
The spread of equipment for office and factory automation has become quite pronounced in recent years. Such equipment is extremely effective but inadvertent or careless operation of switches possessed by the equipment can lead to a major accident. For example, if the power supply switch of a device such as a word processor is inadvertently turned off while the device is in the course of processing important data, which may have taken many long hours and considerable manpower to prepare, the data may be destroyed. There is also the likelihood that erroneous operation of various switches will cause the data to be processed incorrectly.
Problems of the type described will tend to occur with greater frequency as the electronic processing of information becomes more widespread. One approach for dealing with them in the case of a device such as a word processor is to provide the power supply switch at a location where one is constrained to search for it, such as at the side or back of the device. However, disposing the power supply switch in such fashion makes it difficult to use the switch and erroneous operation can still occur if the switch is struck accidentally by some object.
To prevent such accidents from occuring, a power supply or other switch preferably is provided with its own a locking mechanism to prevent erroneous or careless operation.
To this end, and by way of example, the specification of Japanese Utility Model Publication (Kokoku) No. 41-6523 discloses a locking-type push-button switch that requires to be operated in two different directions. Specifically, the switch requires both rotating and pushing operations. Let us describe the structure and operation of this switch in brief with reference to FIGS. 1 through 3.
As shown, the locking-type push-button switch is constituted by a contact unit 5 comprising fixed contacts 1, movable contacts 2, a restoring spring 3 and a shaft 4, a push button 10, a rotary knob 11, a biasing spring 12, an annular leaf spring 13, an attachment fixture 15, and a locking pin 16. The push button 10 is biased downwardly by the spring 12 against the force of the restoring spring 3 in the contact unit 5. The rotary knob 11 has a central bore and includes a lower cylindrical portion 17 the outer surface of which is provided with a circumferentially extending spring receiving groove 14 and a longitudinal groove 18 for mounting the annular leaf spring 13. The lower cylindrical portion 17 has a lower end face in which are formed a V-shaped cam groove 19 and a shallow locking groove 22 contiguous to the V-shaped groove 19, these grooves passing entirely through the cylindrical portion. The attachment member 15 is provided with a central bore the inner surface whereof is provided with a longitudinal groove 20 for positioning and guiding both a projection 21 on the annular leaf spring 13 and the locking pin 16. Though the leaf spring 13 has the projection 21 at opposing positions on its inner and outer side, the spring 13 has an annular configuration overall. The locking pin 16 is for engaging with the V-shaped cam groove 19 and locking groove 22 and is embraced from both sides by the push button 10 and the shaft 4, which is urged upwardly by the restoring spring 3 of contact unit 5.
In operation, finger pressure applied to and removed from the push button 10 causes the locking pin 16 in contact with the push button 10 to be moved up or down while it slides on a vertical surface of the V-shaped cam groove 19, and causes the contacts in the contact unit 5 to changeover. The push button is not locked merely by being pushed. To effect locking, it is also necessary that the rotary knob 11 be rotated in the clockwise direction. When this is done, the locking pin 16, which can travel only up and down along the longitudinal groove 20, moves out of the V-shaped cam groove 19 from its bottom portion and into the locking groove 22 along its inclined surface owing to rotation of the knob 11 and is eventually seated in the locking groove 22. As a result of this series of operations, the locking pin 16 is moved downwardly so as to urge the shaft 4 of the contact unit 5 downwardly against the restoration force of the restoring spring 3. Eventually, the locking pin 16 descends to a position at which balance is achieved between the elastic force of the annular leaf spring 13 and the spring force of the restoring spring 3 in the contact unit 5. The contact unit 5 is changed over when this position is reached. This is the locked state, which is maintained until the rotary knob 11 is turned in the counter-clockwise direction to release the lock.
Thus, in the conventional locking-type push-button switch described above, the direction in which the push button 10 is operated differs from that in which the rotary knob 11 is operated. Though this is effective in terms of preventing erroneous operation, locking is achieved by rotating the knob 11, and this operation is entirely independent of that for working the push button 10. As a result, the switch possesses a complicated structure. In addition, the switch cannot be locked automatically by pressing the push button 10. Locking is accomplished only by rotating the knob 11, which is not operatively associated with the push button 10. Consequently, it is difficult to perform the locking and button depressing operations in concert. In actuality, therefore, preventing erroneous operation of the push button 10 involves some difficulty. Furthermore, one is likely to mistakenly assume that the push-button switch is locked after pressing the push button 10, a lapse that can, in the end, invite erroneous operation of the push button.
Moreover, since the rotary knob 11 is not only for unlocking the switch, the locking function performed by the rotary knob 11 and the circuit changeover function performed by the push button 10 are not clearly distinguished. If the user operates the rotary knob 11 with the intention of locking the switch, the circuit will be switched inadvertently.